Grinding method for grinding back-surface of semiconductor wafer and grinding apparatus for grinding back-surface of semiconductor wafer used in same

ABSTRACT

A grinding method for grinding a back surface of a semiconductor wafer that performs infeed grinding of a back surface of a wafer laminated body, the method, during the grinding of the back surface of the wafer laminated body, having: measuring respectively a thickness of an outer peripheral portion and an inner peripheral portion of the wafer laminated body; calculating a thickness difference between the thickness of the outer portion and the thickness the inner portion; and tilting an axis of a grinding wheel by a predetermined angle in an arbitrary direction so as to reduce the calculated thickness difference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for grinding a back surface of a semiconductor wafer and to an apparatus for grinding a back surface of a semiconductor wafer used in the same method.

2. Description of Related Art

In general, a processing method for reducing thickness of a semiconductor wafer has been known in which a support base material formed of glass, resin, etc., is adhered to the front surface of the semiconductor wafer, and with the semiconductor wafer fixed via the base material to a vacuum chuck on a turn-table, the back surface of the wafer is ground. In this method, for example, a distance from the upper surface of the turn-table to the back surface of the wafer laminated body is measured by using a contact type sensor as an in-process gauge, and grinding and in-process measurement is performed simultaneously without removing the wafer laminated body from the turn-table until the thickness of the wafer reaches to a predetermined dimension.

As an example of related art related to the grinding method for grinding a back surface of a semiconductor wafer according to the present invention, a method is disclosed in Japanese Unexamined Patent Publication No. 2005-205543. Japanese Unexamined Patent Publication No. 2005-205543, in paragraph [0005], includes a description that “. . . in order to grind a wafer, there are several grinding methods for grinding a wafer, and among them, two main methods are a creep feed grinding method in which a wafer is ground by being passed between two cylinder grinding wheels forming a pair, and an infeed grinding method in which a cup shaped grinding wheel is used such that the cup shaped grinding wheel and a wafer are both rotated so as to pass the grinding wheel across the center of the wafer. In particular, the infeed type grinding method is often used in grinding of a semiconductor wafer since higher surface flatness can be more easily obtained than with the creep feed type grinding method.”

Further, in paragraph [0006], there is a description that “Such an infeed type grinding can be performed, for example, by using a grinding device 21 as shown in FIG. 8. This grinding device 21 has a chuck table 23 for holding a wafer by vacuum suction, and a cup type grinding wheel 26 having a grinding head 25 with a grinding wheel 24 fixed thereto, and one surface of a semiconductor wafer can be ground, for example, by sucking the semiconductor wafer 22 to be ground to the chuck table 23 and rotating the wafer, and, while the grinding head 25 is being rotated about the rotation axis 27, pressing the grinding wheel 24 to the wafer 22.”

As a problem related to the problem of the present invention, in paragraph [0005] of Japanese Unexamined Patent Publication No. 2005-205543, there is a description that “on the surface of the ground wafer, grinding striations having a certain periodicity may be formed as the locus of the grinding wheel, or a concave portion having recessed shape may be formed in the center portion of the wafer”. Although the grinding striations on the wafer surface can be removed by subsequent polishing process as a post-processing, there is another problem that the flatness of the wafer may be deteriorated when the amount of polished wafer is increased in the polishing process, and productivity may be lowered.

The problem that a concave portion may be formed in the center portion of the wafer, is considered to arise from complicated interactions of various factors such as the grinding device, the grinding wheel, the support structure for the wafer laminated body, conditions for grinding, the grinding method and the like. The case where a convex portion is formed in the center portion of the wafer is considered to arise in the same manner. The back surface of a wafer formed by relative movement of the grinding wheel and the wafer is thus a result of complicated interaction of various factors, and therefore, it is considered difficult to finish the back surface of a wafer so as to achieve the flatness in a predetermined precision.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a grinding method for grinding a back surface of a semiconductor wafer that can suppress formation of a concave portion or a convex portion in the center portion of the wafer, and that can finish the back surface of the wafer to a desired flatness, and a grinding apparatus for grinding a back surface of a semiconductor wafer that is used in same method.

In order to attain above object, in accordance with the present invention, there is provided a grinding method for grinding a back surface of a semiconductor wafer wherein a wafer laminated body having a support base material adhered to a front surface thereof for protecting a circuit pattern is fixed to a table with the front surface facing downward and a back surface to be ground facing upward, and in this state, while the wafer laminated body is being rotated in a horizontal plane and a grinding wheel is being rotated about its axis, the grinding wheel is moved in a vertical direction at a predetermined feed speed to thereby grind the back surface of the wafer laminated body, the method comprising measuring a thickness of an outer peripheral portion and an inner peripheral portion of the wafer laminated body while grinding the back surface of the wafer laminated body, calculating a thickness difference between the thickness of the outer peripheral portion and the inner peripheral portion, and tilting the axis of the grinding wheel so as to reduce the calculated thickness difference.

In the grinding method for grinding a back surface of a semiconductor wafer, it is also possible to tilt the axis of the grinding wheel so as to achieve a uniform in-plane pressure distribution in a contact plane between the grinding wheel and the wafer laminated body.

In the grinding method for grinding a back surface of a semiconductor wafer, when the thickness of the outer peripheral portion of the wafer laminated body is less than the thickness of the inner peripheral portion of the wafer laminated body, it is also possible to tilt the axis of the grinding wheel so as to achieve the in-plane pressure in the outer peripheral portion of the wafer laminated body that is comparable to or less than the in-plane pressure in the inner peripheral portion of the wafer laminated body.

With the grinding method for grinding a back surface of a semiconductor wafer as described above, by tilting the axis of the grinding wheel based on the thickness of the outer peripheral portion and the inner peripheral portion of the wafer laminated body measured in-process while infeed grinding of the back surface of the wafer laminated body is being performed, it is possible to reduce the thickness difference of the thickness between the outer peripheral portion and the inner peripheral portion of the wafer laminated body. Therefore, it is possible to suppress formation of a concave portion or a convex portion in the center portion of the wafer and to finish the wafer to a desired flatness.

In accordance with another aspect of the present invention, there is provided a grinding apparatus for grinding a back surface of a semiconductor wafer used in the grinding method for grinding a back surface of a semiconductor wafer as described above, comprising a spindle head that supports a grinding wheel having a grinding surface disposed in opposition to a back surface of the wafer laminated body rotatably about the axis, measurement means that measures a thickness of an outer peripheral portion and an inner peripheral portion of the wafer laminated body, angle fine adjustment means for tilting the axis of the grinding wheel relative to a vertical direction, and a controller that receives an input signal from the measurement means, and calculates a thickness difference of the thickness between the outer peripheral portion and the inner peripheral portion to thereby control the angle fine adjustment means so as to reduce the thickness difference.

With the grinding apparatus for grinding a back surface of a semiconductor wafer as described above, by tilting the axis of the grinding wheel based on the thickness of the outer peripheral portion and the inner peripheral portion of the wafer laminated body measured in-process, it is possible to reduce the thickness difference of the thickness between the outer peripheral portion and the inner peripheral portion of the wafer laminated body. Therefore, it is possible to suppress formation of a concave portion or a convex portion in the center portion of the wafer and to finish the wafer to a desired flatness.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiment with reference to appended drawings, in which:

FIG. 1 is a perspective view of a grinding apparatus for grinding a back surface of a semiconductor wafer according to an embodiment of the present invention;

FIG. 2 is a view for explaining the infeed grinding;

FIG. 3 is a view for explaining the state of simultaneous measurement of the outer peripheral portion and the inner peripheral portion of the wafer laminated body by using in-process gauges;

FIG. 4 is a side view of the grinding apparatus for grinding a back surface of a semiconductor wafer;

FIG. 5A is a view for explaining the state of the axis of the grinding wheel tilted anticlockwise;

FIG. 5B is a view for explaining the state of the axis of the grinding wheel tilted clockwise; and

FIG. 6 is a flow chart of the grinding method for grinding a back surface of a semiconductor wafer.

DETAILED DESCRIPTION

A grinding method for grinding a back surface of a semiconductor wafer according to the present invention and a grinding apparatus for grinding a back surface of a semiconductor wafer used in same according to a preferred embodiment of the invention will be described with reference to drawings. FIG. 1 is a view of a representative form of a grinding apparatus for grinding a back surface of a semiconductor wafer according to the present invention, although the present invention is not limited to this embodiment. Grinding apparatus 1 for grinding a back surface of a semiconductor wafer according to this embodiment has apparatus main body la, turn-table 2 for holding wafer laminated body 10 by vacuum suction with chuck 3 of the front surface side of wafer laminated body 10 having support base material 13 adhered thereto, spindle head 4 for rotatably supporting grinding wheel 15. Spindle head 4 as an exemplary form may have a linear movement feed mechanism for moving grinding wheel 15 up and down in a vertical direction, and a rotary mechanism for rotating grinding wheel 15 about vertical axis R2. In this example, a ball screw feed mechanism can be applied as the linear movement feed mechanism, and a servo motor can be applied as the rotary mechanism.

As shown in FIG. 3, individual wafer laminated body 10 held by individual chuck 3 by vacuum suction is detachably held by chuck 3 in the state in which glass base material (support base material) 13 is adhered via a protective film (not shown) to front surface 12 a having a circuit pattern formed thereon, although the present invention is not limited to this embodiment. As an example, the thickness of semiconductor wafer 11 before grinding is about 750 μm, the thickness of a protective film is about 100 μm, and the thickness of a glass base material is about 1 mm. Semiconductor wafer 11 is ground to a predetermined thickness, for example to a thickness as thin as about 30 μm, based on s grinding allowance calculated from the thickness of a single wafer.

Grinding apparatus 1 for grinding a back surface is adapted to be used to perform infeed grinding. As shown in FIG. 2, infeed grinding is performed while both grinding wheel 15 and wafer laminated body 10 are being simultaneously rotated. Thus, grinding wheel 15 mounted to spindle head 4 is disposed in a predetermined positional relation in a horizontal plane (X-Y plane) in opposition to wafer laminated body 10, and wafer laminated body 10 together with chuck 3 is rotated about axis R1, while grinding wheel 15 is being rotated about axis R2 in the same direction as wafer laminated body 10, and in this state, grinding wheel 15 is moved downward in a vertical direction so as to press back surface 12 b of wafer 11 with force F by grinding surface 16 a to thereby perform grinding of back surface 12 b of wafer 11. In FIG. 2, the directions of rotation of grinding wheel 15 and of wafer laminated body 10 are the same, although the direction of rotation of grinding wheel 15 and of wafer laminated body 10 may be different from each other. When the directions of rotation of grinding wheel 15 and of wafer laminated body 10 are the same, grinding resistance is lowered and precision of processing of wafer 11 can be improved, and when the directions of rotation of grinding wheel 15 and of wafer laminated body 10 are different, grinding efficiency can be increased.

Grinding apparatus 1 for grinding a back surface according to this embodiment has several unique features. Grinding apparatus 1 for grinding a back surface according to this embodiment further has in-process gauges 5, 6 (see FIG. 3) for simultaneously measuring the thickness of the outer peripheral portion and the inner peripheral portion of wafer laminated body 10 while grinding wafer back surface 12 b, angle fine adjustment means 12 for tilting axis R2 of grinding wheel 15 relative to the vertical direction, controller 16 that receives input signal from in-process gauges 5, 6 and calculates the thickness difference between the thickness of the outer peripheral portion and the inner peripheral portion, and, based on the calculated thickness difference, controls the servo motor of angle fine adjustment means 12 so as to reduce the calculated thickness difference. The controller has an operation section and an automatic angle adjustment section. In the operation section, it receives the input signal from the contact type sensor and calculates the thickness difference between the thickness of the outer peripheral portion and the inner peripheral portion. In the automatic angle adjustment section, it controls the servo motor of angle fine adjustment means 12 based on a predetermined relation between the calculated thickness difference and the angle of axis R2 of grinding wheel 15.

Each of the components of grinding apparatus 1 for grinding a back surface according to the present embodiment will be described below.

Each in-process gauge 5, 6 as a representative form of measurement means is a measuring instrument in which the change of probe 5 a, 5 b as a contactor is converted to a voltage signal by a differential transformer, and based on the converted voltage signal, the distance between the upper surface of turn-table 2 and back surface 12 b of the wafer, that is, thickness δ of wafer laminated body 10, is monitored in-process (see FIG. 3). Thickness δ varies for individual wafer laminated body 10, but since grinding is performed to a position obtained by subtracting the grinding allowance from thickness δ, individual semiconductor wafer 11 can be ground always to the same thickness without being affected by the tolerance of support base material 13 or the protective film.

The grinding apparatus for grinding a back surface according to the present invention has three in-process gauges 5, 6, 7. In-process gauge 7 is used for measuring the position of the upper surface of turn-table 2, and two in-process gauges 5, 6 are used for measuring the thickness of the outer peripheral portion and the inner peripheral portion of wafer laminated body 10, respectively. By providing two in-process gauges 5, 6, the thickness of the outer peripheral portion and the inner peripheral portion of wafer laminated body 10 can be measured simultaneously in-process, so that non-uniform distribution of grinding pressure in the contact plane of grinding wheel 15 and wafer laminated body 10 can be estimated. The number of the in-process gauges for measuring the thickness of wafer laminated body 10 is not limited to two in the present invention, and three or more in-process gauges may be provided for this purpose.

Turn-table 2 is formed in the shape of a disc, and is provided with four rotatable chucks 3. Individual chuck 3 is adapted to suck with a vacuum pressure glass base material 13 adhered to wafer laminated body 10. Wafer laminated body 10 is thereby held on chuck 3. After grinding of the back surface is completed, air is supplied to chuck 3 so that wafer laminated body 10 can be quickly removed from chuck 3. On the underside of individual chuck 3, output shaft 21 of motor 20 is attached coaxially with the center axis of chuck 3. Individual chuck 3 is adapted to be rotated clockwise by the driving force of motor 20.

Grinding wheel 15 is used for grinding back surface 12 b of semiconductor wafer 10 held in suction on turn-table 2, and a diamond grinding wheel with liquid bond as binder, for example, can be used. By using a liquid bond as a binder, grinding wheel 15 has resilience, and the force of impact at the time of contact of the grinding wheel with wafer laminated body 10 is relaxed, and highly precise processing of back surface 12 b of the wafer can be achieved.

Grinding wheel 15 is attached to spindle head 4 with axis R2 aligned coaxially with the output shaft of the motor (not shown), and is rotated anticlockwise by the driving force of the motor. Truing of grinding wheel 15 is performed on the apparatus, and grinding surface 16 a opposed to back surface 12 b of the wafer is shaped flat. Dressing is performed to regenerate new sharp edges on the surface of grinding wheel 15 with lowered sharpness.

Spindle head 4 has spindle 9 having grinding wheel 15 mounted thereto, a ball screw feed mechanism as a linear movement feed mechanism that moves grinding wheel 15 up and down in a vertical direction, a servo motor that rotates grinding wheel 15 about axis R2, and angle fine adjustment means 12 that tilts axis R2 of grinding wheel 15 relative to a vertical direction. By moving grinding wheel 15 in the direction approaching to semiconductor wafer 11, grinding wheel 15 is abutted to back surface 12 b of semiconductor wafer 11, and a predetermined surface pressure F can be applied to grind back surface 12 b of wafer (see FIG. 2).

FIG. 5A and FIG. 5B are views of axis R2 of the grinding wheel 15 being tilted in-process relative to the vertical direction by angle fine adjustment means 12. As shown in FIG. 5A, when the thickness of the outer peripheral portion of wafer laminated body 10 is less than the thickness of the inner peripheral portion, that is, when a concave portion (not shown) is formed in the center portion of semiconductor single wafer 11 (when the outer peripheral portion of single semiconductor wafer is formed with thickness larger than thickness of the inner peripheral portion), axis R2 of grinding wheel 15 and spindle 9 is tilted anticlockwise by angle θ1 depending on the thickness difference, such that the grinding pressure (in-plane pressure) on the outer peripheral portion of wafer laminated body 10 is comparable to or less than the grinding pressure on the inner peripheral portion of wafer laminated body 10. With such construction, the thickness difference between the outer peripheral portion and the inner peripheral portion of wafer laminated body 10 becomes equal to zero or nearly equal to zero, and the grinding pressure in the contact plane of grinding wheel 15 and wafer laminated body 10 is leveled, and back surface 12 b of the wafer can be formed flat.

On the contrary, as shown in FIG. 5B, when the thickness of the outer peripheral portion of wafer laminated body 10 is greater than the thickness of the inner peripheral portion, that is, when a convex portion is formed in the center portion of single semiconductor wafer 11 (when the outer peripheral portion of single semiconductor wafer is formed with thickness smaller than thickness of the inner peripheral portion), axis R2 of grinding wheel 15 and spindle 9 is tilted clockwise by angle θ2 depending on the thickness difference, such that the grinding pressure (in-plane pressure) on the outer peripheral portion of wafer laminated body 10 is comparable to or greater than the grinding pressure on the inner peripheral portion of wafer laminated body 10. With such construction, the thickness difference between the outer peripheral portion and the inner peripheral portion of wafer laminated body 10 becomes equal to zero or nearly equal to zero, and the grinding pressure in the contact plane of grinding wheel 15 and wafer laminated body 10 is leveled, and back surface 12 b of the wafer can be formed flat.

Next, referring to FIG. 6, the grinding method for grinding a back surface of a semiconductor wafer by using grinding apparatus 1 for grinding a back surface will be described. First, at step S1, wafer laminated body 10 is caused to be sucked to chuck 3 with the front surface of wafer laminated body 10 faced downward and the back surface of wafer laminated body 10 faced upward. At step S2, thickness δ of wafer laminated body 10 integral with glass base material 13 is measured by using an in-process gauge or an IR sensor on the apparatus, and the grinding allowance is obtained by subtracting the final thickness of wafer 11 from thickness δ of wafer laminated body 10. The grinding allowance is inputted to the controller in order to control grinding apparatus 1 for grinding a back surface with respect to grinding allowance.

Then, at step S3, the turn-table 2 is rotated, and the wafer laminated body 10 is positioned so as to bring the wafer laminated body 10 and the grinding wheel 15 in opposition to each other. Next, at step S4, the wafer laminated body 10 is rotated by the motor 20, and while the grinding wheel 15 attached to the spindle head 4 is being rotated by a motor, the ball screw is driven to move the grinding wheel 15 downward and to bring the grinding surface 16 a into pressing contact with the back surface of the semiconductor wafer 11 to grind the back surface 12 b of the wafer.

At step S5, while the back surface of the wafer is being ground, the thickness of the outer peripheral portion and the inner peripheral portion of wafer laminated body 10 is measured by using in-process gauges 5, 6 in region where wafer laminated body 10 does not come into contact with grinding wheel 15. After the thickness difference between the thickness of the outer peripheral portion and the inner peripheral portion of wafer laminated body 10 is calculated at step S6 in the operation section of unshown controller, axis R2 of grinding wheel 15 and spindle 9 is tilted by a predetermined angle in an arbitrary direction so as to reduce the calculated thickness difference at step S7.

Finally, at step S8, with axis R2 of grinding wheel 15 and spindle 9 tilted as described above, back surface 12 b of the wafer is processed by a predetermined grinding allowance, and the processing of the back surface is completed.

After grinding has been completed, with wafer laminated body 10 fixed to chuck 3, polishing is performed by using an unshown polishing device in order to remove the layer damaged by the grinding. Damages such as unintended cracks of wafer 11 can be thereby prevented. After polishing has been completed, wafer laminated body 10 is removed from chuck 3 and transferred to next processing step, and coating or dicing step is performed.

Thus, with the grinding method for grinding a back surface of a semiconductor wafer and the grinding apparatus for grinding a back surface of a semiconductor wafer used in same, while wafer laminated body 10 is being ground, axis R2 of grinding wheel 15 and spindle 9 can be tilted by a predetermined angle in an arbitrary direction based on the thickness of the outer peripheral portion and the inner peripheral portion of wafer laminated body 10 measured in-process so as to level the grinding pressure in the contact plane of grinding wheel 15 with wafer laminated body 10, and back surface 12 b of the wafer can be formed flat.

The present invention is not limited to the embodiment as described above, but may be implemented in various modifications without departing from the scope and spirit of the invention. In the present embodiment, wafer laminated body 10 is composed of semiconductor wafer 11, a protective film and glass base material 13, although the wafer laminated body may be composed of a semiconductor wafer, a protective film and a resin base material, as another embodiment. Liquid adhesive may be used in place of a protective film for adhering semiconductor wafer 11 and base material 13 to each other.

Grinding apparatus 1 of the present embodiment has in-process gauges 5, 6, although other measurement means may be used as long as a thickness of wafer laminated body 10 fixed to turn-table 2 can be measured. 

1. A grinding method for grinding a back surface of a semiconductor wafer, wherein a wafer laminated body having a support base material adhered to a front surface of said semiconductor wafer for protecting a circuit pattern formed on said front surface is fixed to a table with a front surface faced downward and with a back surface to be ground faced upward, and wherein, while said wafer laminated body is being rotated in a horizontal plane and a grinding wheel is being rotated about a axis of said grinding wheel, said grinding wheel is moved in a vertical direction at a predetermined feed speed to thereby grind said back surface of said wafer laminated body; said method, during grinding of said back surface of said wafer laminated body, comprising: measuring respectively a thickness of an outer peripheral portion and an inner peripheral portion of said wafer laminated body; calculating a thickness difference between said thickness of said outer portion and said thickness of said inner portion; and, tilting said axis of said grinding wheel so as to reduce the calculated thickness difference.
 2. A grinding method for grinding a back surface of a semiconductor wafer according to claim 1, wherein said axis of said grinding wheel is tilted such that in-plane pressure distribution in the contact plane of said grinding wheel and said wafer laminated body becomes uniform.
 3. A grinding method for grinding a back surface of a semiconductor wafer according to claim 1, wherein, when said thickness of said outer peripheral portion of said wafer laminated body is less than said thickness of said inner peripheral portion of said wafer laminated body, said axis of said grinding wheel is tilted such that said in-plane pressure in said outer peripheral portion of said wafer laminated body is comparable to or less than said in-plane pressure in said inner peripheral portion of said wafer laminated body.
 4. A grinding apparatus for grinding a back surface of a semiconductor wafer, comprising: a spindle head for supporting a grinding wheel having a grinding surface disposed in opposition to said back surface of a wafer laminated body rotatably about an axis of said grinding wheel; a measurement means for measuring respectively a thickness of an outer peripheral portion and a thickness of an inner peripheral portion of said wafer laminated body; an angle fine adjustment means for tilting said axis of said grinding wheel relative to a vertical direction; and, a controller that receives input signal from said measurement means, calculates a thickness difference between said thickness of said outer peripheral portion and said thickness of said inner peripheral portion, and controls said angle fine adjustment means so as to reduce said thickness difference. 